How to reduce harmonic on PCB ?

I want to Know, how to reduce harmonic on PCB layout, hope someone can
help me or offer some paper to me .

thanks a lot!

Is this a trick question? Use a lowpass filter.

To reduce harmonies, I guess you meant noise. It can be reduce with proper placement and grounding techniquies. From there, if the intended signal to nosie ratio is still possible then maybe not have to use a low pass filter.

I assume you have meant EMC/noise ..

In this case have a look at this publication:
http://alternatezone.com/electronics...torialRevA.pdf
Especially, read sections on the following subjects (page 18 +++):
Power Planes
Good Grounding
Good Bypassing
High Frequency Design Techniques

And, on "A PCB design approach for best EMC" goto: http://www.ieee.org.uk/docs/emc0604a.pdf

Regards,
IanP